I have been told I show no feelings, too. And you are right, it is like on/off, all/nothing.
We turn our emotions off on purpose sometimes as a way of protecting ourselves. We receive everything around us as input, add all emotions responses and we overflow. So yes, we show and feel nothing sometimes because we have to. We have an all or nothing valve, we can't filter as others do.
This is as it is for me, I have accepted it now.